Disks for use in computer memory storage devices, such as disk drives, have been manufactured for some years by sputtering or otherwise placing magnetic media on both sides of a disk. Disks made of aluminum or other metals and alloys, plastics, glass and ceramic have been employed. The diameter and thicknesses of the disks have become progressively smaller and thinner typically going from 130 mm to 95 mm to 65 mm to 48 mm and less in diameter and having thicknesses of 1.98 mm for a 130 mm disk to 0.38 mm for a 48 mm disk (or thinner). The aluminum disks typically are coated with a magnetic media such as 20% Co, 70% Ni and 10% Pt sputtered essentially over all of the planar surfaces of the disk, as described in U.S. Pat. No. 5,244,555. Glass disks are utilized for their superior flatness and surface hardness, the latter to resist "dings" from processing or slider impacts and resultant damage to the disk surface.
Thinner disks are desirable since, among other things, they allow the stacking of more disks in the standard height of a disk drive or an overall reduction in drive height. The resultant thinner and smaller disks have less mechanical strength and can be deformed, cracked or otherwise damaged upon being subjected to various forces.
Current technology for holding disks during certain processing steps such as burnishing and texturing and quality control and development testing has involved the use of expanding mandrels or pressurized bladders which are inserted into a central disk aperture and expanded against the inner peripheral edge of the disk, to hold and clamp the disk. The force (F.sub.1) exerted by such mandrels or bladders is directed radially, that is, in a direction generally parallel to the planar surfaces of the disk. Typically, the central disk aperture is bounded by an inner cylindrical peripheral edge and chamfered surfaces connecting each of the disk's planar surfaces (sides) to that cylindrical peripheral edge. Chamfered edges also facilitate the mounting and centering of the disk on a disk drive spindle. The chamfer also minimizes stress concentrations at the aperture edges and prevents build-up of coated material at the inside diameter (ID) of the disk.
One problem in the prior art is that the force F.sub.1 (shown in FIG. 1) is concentrated by the prior art clamps over a very small area of the disk aperture, namely, on less than the entire cylindrical peripheral edge which may have a width of about 60% of the thickness of the disk. The net result is that the expanding force F.sub.1, applied during disk processing can easily reach a threshold level sufficient to cause deformation of the disk. This deformation includes nick marks at the disk ID and bending or warping of the disk (i.e. the disk going out of flat), and is particularly evident when the clamped disk is rotated at its typical rotation speed of about 2000 rpm or faster. The current fly heights of the read/write heads employed in modern disk drives are at a level of about 2.0 microinches (0.000051 mm).
Deformation from prior art clamping techniques can reach or exceed this height causing head crashing. Further, nick marks at the ID of the disk often result in defective assembly and uneven processing. The prior art clamps are particularly disadvantageous when glass or ceramic disks are being clamped. Glass or ceramic disks tend to have dendritic crystallized surface sites which under a sufficient and normal F.sub.1 force can start disk cracking and breaking. These deformations, damages and breakages have caused relatively high and undesirable reject rates of disks undergoing processing and testing. Thus a need has arisen for the ability to clamp a disk with sufficient clamping force to undergo the necessary disk processing while minimizing the possibility of disk damage.
Furthermore, as disk drive manufacturers seek to expand the limit of the data which can be stored on magnetic disks, there is a commensurate effort to maximize the useable storage space on the disk planar sides. Therefore, in addition to controlling the force exerted on the disk so as to minimize damage during processing, it is necessary to clamp the disk for processing in such a manner so as to minimize interference with the disk planar sides and to avoid blocking the processing of any part of those planar sides.